A direct comparison of performance between 1.9 and 2.x is tricky because they are so different. The closest I have seen is the work by Frederic Nevers. See the discussion "Two recent blog posts on performance" https://moodle.org/mod/forum/discuss.php?d=215569 in the "Hardware and Performance" forum.
General developer forum
Moodle performance 1.9 versus 2.x (25% drop)
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